Method of applying adherent electroplates to zirconium surfaces



United States Patent Q ME H Q AIPLY NG ADHE E PLATES T SURFACES John ac wi iamfii fis ic ueh. and-Charles. Faust, Columbus, 0l 1 io, assign9rsto the United States of America as representedby the United States Atomic Ene g Cmum ss m e w No Drawing. Apglieation May-15, 1953,; o.

Serial 355.853

6 Chime, (G1.- itli-QZ} The present invention relates to a method forcl eauing zirconium surfaces and applying adherent electrodeposits on zirconium surfaces.

It is well known that zireoniummetal readily forms a p e eet e Oxide tha sis s remo a y o na methods. None of the conventional methods for cleaning oth aces. prior. to Q QQQ JQEEQQEL. such as e: co ventional processes for carbon steel, stainlessstee t can successfully applied t theu 'eua n Qt z conium for electroplating Eleetroplates'applied to zirconium after the zirconium is cleanedvbyconventionalmeans for preparing the usual metals of commerce. res sultin electroplates'that can be. easily peeled from the zirconium surface.

The poorly adherent quality ofelectrodepositson zirconium prepared by conventional methods becomes especially apparent upon heat treatment of the compositeare ticle. The heat treatment of poorly adherent electroplated articles will result in a separation of the elect-roplate from. the basis metal. tors, one factor which it isbelieved. contributes in a great part to this is the formation of molecular hydrogen at the interface of thebasis metal. andelectroplate andits expansion during heat treatment which results in lo.-. calized blistering or over-all separation. of? the electro- 40 plate from the basis metal."

It is an object of the present invention to provide'a method for cleaning zirconium and zirconium alloy: sure. faces. I 7

It is another object of the present invention to. provide a method for platingzirconium surfaces. with: highlyadherent metallic electroplates. r

It is a further object ofthe presentinvention topro.-.. vide a method of etching zirconium or zirconiunralloy surfaces for electroplating with another metal so that the 5 as-plated adhesion of theelectrodeposited metal to the zirconium is maintained during heat treatment to alloy the interfacial layersof the twometals.

Other objects will be apparent from the description. of the present invention which follows.

In accordance with the; present invention it. has; been; found that zirconium and zirconium alloys. can; b5261 J cally cleaned by etching the, surface of Said. metal W th...

an aqueous solution of ammonium. fluoride. and-hydro fluoric acid. The etching ofthezirmniuma metalsurface. 9 or zirconium alloy surface. in accordance with the method. described in the present application will providea SUI?- face upon which can. be electroplated auadherent; coat: ing of er m als- The.- tch ng f; irc nium; e zis eenium alley s r s is, all-esse tial. en: ..e.-me.thod; of applying adherent electroplates to zirconium or zir-. um a ley surf ces; c rdanc w th the. proce s. of the present invention. The complete; pr cessfqr-applying her nt lectroplate to. i zirc uium-sunfaceseomr prises broadly three prescribed operations; etching; the

While this may be due to. several face 35' ice],

V V p 2. suriace of the basis metal with an ammopium fluoridehydrofluoric acid bath, fel ectr oplating the plating. in ai on the surface of said; zirconium metal and'heatetreat ing the composite article.

The basis metal contemplated by the present invention includes substantially pure zirconium and zirconium a1- lusts. containing'.. predominantly zirconium. The; surface of: the zirconium or zirconium. alloyshould hezffiGQfofi rolling scale or heat-treating scale," since such scalesare less-solublev in. the etching: solution thanv is theunderlying metal; The method is applicable to. zirconium surfaces which have been finished by substantiallyi all conventional methc ads,v such. a isand or vaporblasting,.-shaping, g:s r- 7 face grinding, or cheniicalpolishing.

Iiheietching solution'of the presentinvention conta prises an aqueous solution by hydrofluoricacideeme monium fluoride .Althohghzircoriium an zirconium alloys: are readily! soluble-in} aqueous solutions of hy-. droiiucric acid, electroplated metals onto. zirconium. sure faces etched in solutions containing; hydrofluoric .acidi aloneiartepoorly adherent and can,v be-easilypeele'd. The,

presence. of: ammoniiunfluoride-lin the etchant" is there: e

molar ratio of ammonium fluoride; toihydrofluorieacid lies between" 11.2 and; 33.0..

While we do not wish to bebou'nd by any theorytade vauced; it is belieyedthat anuetchant'lying within these particul rratios. furnishes .the maximum inhibitionagainst: the; adsorption bythe=zirconium surfacesoftliehydrogen f produced duringthe etching operation. It: is presumably the; adsorbed; hydrogen thatcauses detrimental embrittlee.

ment of the interface during: the subsequent electroplating ofa metal uponthe zirconium; It has; furtherbeenfound, in; accprdancegwiththe present. invention that the; addition al p aticamine. of: he formula;

to. the eteh nasc ut un extend th pr err d te se of,

zirconium removed by. etching will: depend upon the time of immersion inthe etching solution and the tem-l perature of the etching solution. Immersion times of 10 to 240 seconds and solution temperatures of 70 to 120 F. are satisfactory for the pretreatment of zirconium objects to be electroplated. with metals. However; an

mme si ume 0t 0 t econds and. a solutiontemperature. of h. are. pref r. ed

. .lheiefiicieuey offth j. etching step. as a tep th V Rru es c leetr p e in n to zirconium; ur aces has been tested for .vario, olfarratios of ammonium fluoride/hydrogen fluoride by carrying out step then. electroplatinga metal such as nickel on the surface an d determiningthefstress (in pounds per square inch)? required to separate the plating from the basis metal atthe 'interface. r The following examples -illustr-ate'theditference inthe as plated adhesion versus the composition of 'the etching solution in detail; l

P nt une As-plated Ounces Example NHrF Mole/ HF, Mole] NHiF/HF, Ingredients Number Liter iter Molar Ratio g g f Pergamn 5 Nickel sulfate, NlSO4-7H2O 44 0.00 0. 50 1, 000 Nickel chloride, NlClrfiHzO.-- 6.1 0.44 to 0.88 0.44 to 0.88 1.0 1,000 Boric acid, HtBOs 5.0 0.48 to 0.96 0.40 to 0.80 1.2 6, 000 H1O: added as needed to prevent pitting 0.66 to 1.32 0.22 to 0.44 3.0 6,000

0. s3 0. 05 16. 6 1,000 1,000 at a pH of 2.0, a temperature of 140 F. and a current density of 40 amperes per square foot. The composite As shown by Examples 3 and 4, the best as-plated adhesion (6000 p. s. i.) was obtained on zirconium etched in solutions with NH4F/HF molar ratios of 1.2 to 3.0.

After the surface of the metal is etched the metal is then rinsed. This may be accomplished in an aqueous rinse or other conventional rinsing baths.

The surface preparation of zirconium and zirconium alloy objects by etching in accordance with the foregoing procedure is sufficient preparation for electroplating most metals upon the zirconium from conventional baths for electroplating the particular plating metal. The above etching step is particularly suitable for preparing zirconium and zirconium alloy surfaces for subsequent plating by a metal of the transition group of the fourth period of the periodic table, such as iron, cobalt or nickel. Conventional nickel and iron plating baths may be used to electroplate the zirconium object. The asplated adhesion of the electroplated transition metal is greatly improved by heat treatment to diffuse the plating metal and the zirconium or zirconium alloy and thereby produce strong alloy bonds which will resist stresses as great as 40,000 to 50,000 p. s i. Difiusion-bonded nickel or iron to zirconium is a satisfactory basis for subsequent electroplating of the composite object with other metals.

The alloy bonds between zirconium and the electroplating are formed by heating the plated zirconium object to elevated temperatures for a substantial time; for example a transitional metal-plated zirconium object can be heated from 5 to 60 minutes at temperatures from 1250 to 1600 F. The strongest alloy bonds between electroplated nickel and zirconium are formed in 10 to 45 minutes at 1300 F. The strongest alloy bonds between electroplated iron and zirconium are formed in 10 to 45 minutes at 15000 F. Alloying was not apparent at 1100 F. and diffusion at higher temperatures is difficult to control.

It is desirable to pretreat the composite electroplated article before subjecting it to high temperatures. For example, zirconium-electroplated nickel or iron composites are prebaked at 400 F. for more than one hour in order to remove codeposits of hydrogen. Storing the composite at room temperature for several weeks is also an eflective pretreatment to prevent blistering during subsequent diffusion heat treatment.

Now that we have described the process of the present invention, it may be further illustrated by the following examples.

Example I article was pre-baked at 400 F. for 1 /2 hours. then heat-treated for minutes at 1300 F.

Example 11 It was Ounces Ingredlents per gallon Ferrous sulfate, FeSOM'HzO 40 Ferrous chloride, FeClr4H1O 5. 4 Boric acid, H33 03 4. 0 Ammonium sulfate, (NHQZS 2.0 Sodium formats, HOOONa- 2. 0 Wetting agent (sodium lauryl sulfate), 01:13:50 S OaNa. 0. 13

at a pH of 4.0,-a. temperature of 140 F. and a current density of 40 amperes per square foot. Upon completion of the plating operation, the composite article was removed from the bath and stored for two weeks at room temperature. It was then heat-treated for 30 minutes at 1500 F.

The foregoing process, while it has been described as applying to zirconium metal and zirconium alloys, is of course equally applicable to hafnium. In all steps of the present method hafnium and hafnium alloys react in exactly the same manner. as zirconium and zirconium alloys, so that hafnium and hafnium alloys may be cleaned and plated in exactly the same manner as zirconium.

The foregoing disclosure and examples are merely illustrative of the process of the present invention, but the scope of the present invention is not to be limited thereby 7 where n lies between 12 and 18, inclusive.

2. The method of applying an adherent metal coating to a zirconium material object which comprises physically cleaning the surface of said object, then immersing said object in a zirconium etching composition comprising an aqueous solution containing ammonium fluoride and hydrogen fluoride in a molar ratio of between 1.2 and 3.0, inclusive, for 10 to 240 seconds at a temperature of to F., then removing said article from the etching solution and rinsing the surface of said object with water, then electroplating said zirconium object with a metal, then heat-treating the composite object by heating for 10 to 45 minutes at a temperature between 1200 and 1600 F. 1

3. The process of claim 2 wherein the electroplated metal is an iron group metal.

4. The process of claim 2 wherein the electroplating metal is nickel.

2,711,389 5 1 '6') 5. The process of claim 2 wherein the electroplating v [FfRfflliEllCeS Citfidill thefile of this patent metal is iron. a UNI ED- AT PAT 6. A method of chemically cleaning zirconium mate- ST ES ENTS rial surfaces comprising immersing the article to. be, 0, 4 Chu h -----7- 1360- Q 1932:

cleaned in a bath containing between 0.25 and 10% 1, 4 3, ;1 a V of an aliphatic aminehaving the formula CnI-I2nA 1NH2, j FOREIGN PATENTS where n has a value of 12 to 18 inclusive, and ammo- 259 07 1 :G nium fluoride and hydrofluoric acid in a molar ratio of 5 I t ammonium fluoride to hydrogen fluoride of 1 to 3 for l at least 10 seconds at a temperature of 70 to 120 F. 10 i 

1. A ZIRCONIUM MATERIAL ETCHANT COMPRISING AN AQUEOUS SOLUTION CONTAINING 0.44 TO 1.32 MOLES PER LITER AMMONIUM FLUORIDE AND 0.44 TO 0.88 MOLES PER LITER HYDROFLUORIC ACID, THE AMMONIUM FLUORIDE TO HYDROFLUORIC ACID RATIO LYING BETWEEN 1 AND 3, INCLUSIVE, AND 0.25 TO 1 PER CENT OF AN ALIPHATIC AMINE HAVING THE FORMULA 